Optical isomers of an iloperidone metabolite

ABSTRACT

The present invention relates to novel isomers of a metabolite of Iloperidone, their preparation, their use as pharmaceuticals and pharmaceutical compositions containing them.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent application Ser. No. 10/488,128, filed 16 Sep. 2004, which is hereby incorporated herein.

The present invention relates to novel isomers of a metabolite of Iloperidone, their preparation, their use as pharmaceuticals and pharmaceutical compositions containing them.

More particularly, the invention relates to optical isomers of the metabolite P-88-8991 of Iloperidone.

Iloperidone is an atypical antipsychotic developed for the treatment of schizophrenia, having functional affinity for noradrenergic, dopaminergic and serotoninergic receptors. See for example Richelson E. and Souder T, Life Sciences, 68:29-39 (2000).

P-88-8991 is a major circulating metabolite of Iloperidone in human plasma, having the formula A

See for example Mutlib A E et al., Drug Metab. Dispos; 23(9):951-964 (1995). P-88-8991 has been shown to have plasma levels in human about 1.5 fold higher than the parent drug. It is roughly as active as Iloperidone.

P-88-8991 consists of a mixture of two enantiomers which have never been disclosed in the literature. It has now surprisingly been found that humans produce only one enantiomer stereospecifically following administration of Iloperidone.

In the first aspect, the invention provides the enantiomers (R)-P-88-8991 and (S)-P-88-8991 of formulae I and II

in free base or acid addition salt form.

In a further aspect, the invention provides a process for the production of the compounds of formulae I and II, comprising the reduction of Iloperidone of formula III

with an optically active boran complex of formula IV

The compound (S)-1-(4-{3-[4-(6-fluoro-benzo[d]isoxazol-3-yl)-piperidin-1-yl]-propoxy}-3-methoxy-phenyl)-ethanol of formula I is obtained using the boran complex of (3aR,7R}-1-methyl-3,3-diphenyl-tetrahydro-pyrrolo[1,2-c][1,3,2]oxazaborole of formula IVa

whereas the compound (R)-1-(4-{3-[4-(6-fluoro-benzo[d]isoxazol-3-yl)-piperidin-1-yl]propoxy}-3-methoxy-phenyl}ethanol of formula II is obtained using the boran complex of (3aS,7R)-1-methyl-3,3-diphenyl-tetrahydro-pyrrolo[1,2-c][1,3,2]oxazaborole of formula IVb

The reactions can be effected according to conventional methods, e.g. as described in the Examples.

Working up the reaction mixtures and purification of the compounds thus obtained may be carried out in accordance to known procedures.

Acid addition salts may be produced from the free bases in known manner, and vice-versa. Suitable acid addition salts for use in accordance with the present invention include for example the hydrochloride.

The boran complexes used as starting materials can be produced from the corresponding compounds of formula Va and Vb

according to known procedures, e.g. as described in the Examples.

The starting materials of formulae Va and Vb are known.

The compounds of formulae I and II and their pharmaceutically acceptable acid addition salts, hereinafter referred to as agents of the invention, exhibit valuable pharmacological properties when tested in vitro and in animals, and are therefore useful as pharmaceuticals.

In particular the agents of the invention display high affinity for adrenergic α₁ and α_(2c) receptors (pK_(i) 8.9 and 7.8 respectively, for the compound of formula I, and 9.2 and 7.7 respectively, for the compound of formula II), high affinity for 5HT_(2A) and 5HT₆ receptors (pK_(i) 8.9 and 8.1 respectively, for the compound of formula I, and 8.9 and 7.8 respectively, for the compound of formula II) and moderate affinity for the D₂ family (pK_(i) 7.4 to 7.6 for the compound of formula I and 7.4 to 7.8 for the compound of formula II).

Receptor affinity is determined with standard radioligand binding techniques, using human recombinant receptors and native rat brain receptors. Blockade of dopamine D₂ and noradrenergic α_(2c) receptors is tested in cell-lines using luciferase reporter gene assays based on 2nd messenger responses.

In vivo, the agents of the invention exhibit antipsychotic activity, as assessed in standard tests such as the amphetamine-induced hypermotility and the phencyclidine-induced hyperlocomotion tests.

The amphetamine-induced hypermotility test is performed according to the method described by Arnt J in Eur. J. Pharmacol. 283, 55-62 (1995). In this test, the agents of the invention significantly inhibit the amphetamine-induced locomotion of the animals at doses of about 0.01 to about 10 mg/kg s.c.

The phencyclidine-induced hyperlocomotion test is performed according to a rat adaptation of the method described by Gleason S D and Shannon H E in Psychopharmacol. 129, 79-84 (1997). In this test, the agents of the invention significantly block the phencyclidine-induced hyperlocomotion of the rats at doses of about 0.01 to about 10 mg/kg s.c.

The agents of the invention are therefore useful for the treatment of psychotic disorders such as schizophrenia and bipolar disorders.

For the above-mentioned indications, the appropriate dosage will of course vary depending upon, for example, the compound employed, the host, the mode of administration and the nature and severity of the condition being treated. However, in general, satisfactory results in animals are indicated to be obtained at a daily dosage of from about 0.1 to about 500, preferably from about 0.5 to about 100 mg/kg animal body weight. In larger mammals, for example humans, an indicated daily dosage is in the range from about 1 to about 500, preferably from about 1 to about 300 mg of an agent of the invention, conveniently administered, for example, in divided doses up to four times a day or in sustained release form.

The agent of the invention may be administered by any conventional route, in particular enterally, preferably orally, for example in the form of tablets or capsules, or parenterally, for example in the form of injectable solutions or suspensions.

The agents of the invention may alternatively be administered e.g. topically in the form of a cream, gel or the like, or by inhalation, e.g. in dry powder form.

Examples for compositions comprising an agent of the invention include, e.g. a solid dispersion, an aqueous solution, e.g. containing a solubilising agent, a microemulsion and a suspension of an agent of the invention. The composition may be buffered to a pH in the range of e.g. from 3.5 to 9.5, by a suitable buffer.

The agents of the invention can be administered either alone or in combination with other pharmaceutical agents effective in the treatment of psychotic disorders such as schizophrenia or bipolar disorders. The present invention thus provides a combination comprising a therapeutically effective amount of an agent of the invention and a second drug substance, for simultaneous or sequential administration.

In accordance with the foregoing, the present invention also provides an agent of the invention, for use as a pharmaceutical, e.g. for the treatment of psychotic disorders.

The present invention furthermore provides a pharmaceutical composition comprising an agent of the invention in association with at least one pharmaceutical carrier or diluent. Such compositions may be manufactured in conventional manner. Unit dosage forms contain, for example, from about 0.25 to about 150, preferably from 0.25 to about 25 mg of a compound according to the invention.

Moreover the present invention provides the use of an agent of the invention, for the manufacture of a medicament for the treatment of psychotic disorders.

In still a further aspect the present invention provides a method for the treatment of psychotic disorders in a subject in need of such treatment, which comprises administering to such subject a therapeutically effective amount of an agent of the invention.

The following examples illustrate the invention.

EXAMPLE 1 (S)-1-|4-{3-f4-(6-Fluoro-benzo[d]isoxazol-3-yl)-piperidin-1-y11-propoxy}-3-methoxy-phenyl)ethanol

56.36 g of boran complex of (3aR,7R)-1-methyl-3,3-diphenyl-tetrahydropyrrolo[1,2c][1,3,2]oxazaborole (1 equivalent) is dissolved under nitrogen in methylenehloride, and the solution is cooled to 0° C. A 1M solution of 1-(4-{3-[4-(6-fluoro-benzo[d]isoxazol-3-yl)piperidin-1-yl]-propoxy}-3-methoxy-phenyl)-ethanone (Iloperidone; 1 equivalent) in methylenehloride is added via a dropping funnel over 90 minutes while the internal temperature is maintained at 0° C.±2° C. After the addition is complete, the mixture is stirred at 0° C. for 20 hours. The reaction mixture is then poured into precooled methanol (0-5° C.) during 1 hour. The solution is warmed to room temperature and stirred until the H₂ evolution ceases. The solution is concentrated by distillation and the residue dried in vacuum, treated with methanol and stirred for about 1 hour at 50° C. and an additional hour at 0° C. The product is isolated by filtration and dried under reduced pressure for 3 hours at 50° C. The title compound is obtained (white crystals).

[α]_(D) ²⁰−19.3° (c=1 in chloroform)

Mp: 138.2-138.8° C.

The boran complex used as starting material can be obtained as follows:

200 mL of a solution of (3aR,7R)-1-methyl-3,3-diphenyl-tetrahydro-pyrrolo[1,2c][1,3,2]oxazaborole (1M in toluene) is stirred at room temperature under nitrogen. 1.2 equivalent borane-dimethylsulfide complex is added with a syringe. The solution is stirred for 2 further hours at room temperature. The borane complex is then crystallised by addition of 4 vol dry hexane and cooling to −12° C. for 1.5 hour. The product is isolated by filtration in a sintered glass funnel and dried in vacuum at 40° C. The boran complex is obtained (white crystals).

EXAMPLE 2 (R)-1-(4-{3-[4-(6-fluoro-benzo[d]isoxazol-3-yll-piperidin-1-yl]-propoxy}-3-methoxy-phenlyl)ethanol

This compound is produced in analogy to Example 1, using boran complex of (3aS,7R)-1-methyl-3,3-diphenyl-tetrahydro-pyrrolo[1,2-c][1,3,2]oxazaborole.

[α]_(D) ²⁰=+18.4° (c=1 in chloroform)

Mp: 137.9-138.3° C. 

1. A pharmaceutical composition for treating a psychotic disorder in a human consisting essentially of (S)-1-[4-{3-[4-(6-fluoro-benzo(d)isoxazol-3-yl)-1-piperidin-1-yl]propoxy}-3-methoxy-phenyl]-ethanol or a pharmaceutically acceptable salt thereof.
 2. A pharmaceutical composition for treating a psychotic disorder in a human consisting essentially of (S)-1-[4-{3-[4-(6-fluoro-benzo(d)isoxazol-3-yl)-1-piperidin-1-yl]propoxy}-3-methoxy-phenyl]-ethanol prepared by enantioselective reduction of iloperidone.
 3. The pharmaceutical composition of claim 2, wherein the reduction is effected by contact of iloperidone with an optically-active borane complex of formula IV


4. A method for treating a psychotic disorder in a human subject in need of such treatment, the method comprising administering to the subject a therapeutically-effective amount of (S)-1-[4-{3-[4-(6-fluoro-benzo(d)isoxazol-3-yl)-1-piperidin-1-yl]propoxy}-3-methoxy-phenyl]-ethanol or a pharmaceutically acceptable salt thereof. 